Effects of dietary fat on gut microbiota and faecal metabolites, and their relationship with cardiometabolic risk factors: a 6-month randomised controlled-feeding trial.

OBJECTIVE: To investigate whether diets differing in fat content alter the gut microbiota and faecal metabolomic profiles, and to determine their relationship with cardiometabolic risk factors in healthy adults whose diet is in a transition from a traditional low-fat diet to a diet high in fat and reduced in carbohydrate. METHODS: In a 6-month randomised controlled-feeding trial, 217 healthy young adults (aged 18-35 years; body mass index <28 kg/m2; 52% women) who completed the whole trial were included. All the foods were provided during the intervention period. The three isocaloric diets were: a lower-fat diet (fat 20% energy), a moderate-fat diet (fat 30% energy) and a higher-fat diet (fat 40% energy). The effects of the dietary interventions on the gut microbiota, faecal metabolomics and plasma inflammatory factors were investigated. RESULTS: The lower-fat diet was associated with increased α-diversity assessed by the Shannon index (p=0.03), increased abundance of Blautia (p=0.007) and Faecalibacterium (p=0.04), whereas the higher-fat diet was associated with increased Alistipes (p=0.04), Bacteroides (p<0.001) and decreased Faecalibacterium (p=0.04). The concentration of total short-chain fatty acids was significantly decreased in the higher-fat diet group in comparison with the other groups (p<0.001). The cometabolites p-cresol and indole, known to be associated with host metabolic disorders, were decreased in the lower-fat diet group. In addition, the higher-fat diet was associated with faecal enrichment in arachidonic acid and the lipopolysaccharide biosynthesis pathway as well as elevated plasma proinflammatory factors after the intervention. CONCLUSION: Higher-fat consumption by healthy young adults whose diet is in a state of nutrition transition appeared to be associated with unfavourable changes in gut microbiota, faecal metabolomic profiles and plasma proinflammatory factors, which might confer adverse consequences for long-term health outcomes. TRIAL REGISTRATION NUMBER: NCT02355795; Results.

Effect of oligosaccharides on the adhesion of gut bacteria to human HT-29 cells.

The influence of five oligosaccharides (cellobiose, stachyose, raffinose, lactulose and chito-oligosaccharides) on the adhesion of eight gut bacteria (Bifidobacterium bifidum ATCC 29521, Bacteroides thetaiotaomicron ATCC 29148D-5, Clostridium leptum ATCC 29065, Blautia coccoides ATCC 29236, Faecalibacterium prausnitzii ATCC 27766, Bacteroides fragilis ATCC 23745, Clostridium difficile ATCC 43255 and Lactobacillus casei ATCC 393) to mucous secreting and non-mucous secreting HT-29 human epithelial cells, was investigated. In pure culture, the bacteria showed variations in their ability to adhere to epithelial cells. The effect of oligosaccharides diminished adhesion and the presence of mucus played a major factor in adhesion, likely due to high adhesiveness to mucins present in the native human mucus layer covering the whole cell surface. However, clostridia displayed almost the same level of adhesion either with or without mucus being present. Bl. coccoides adhesion was decreased by stachyose and cellobiose in non-mucus-secreting cells in pure culture, while in mixed faecal culture cellobiose displayed the highest antiadhesive activity with an overall average of 65% inhibition amongst tested oligomers and lactulose displayed the lowest with an average of 47.4%. Bifidobacteria, Bacteroides, lactobacilli and clostridia were inhibited within the following ranges 47-78%, 32-65%, 11.7-58% and 64-85% respectively. This means that clostridia were the most strongly influenced members of the microflora amongst the bacterial groups tested in mixed culture. In conclusion, introducing oligosaccharides which are candidate prebiotics into pure or mixed cultures has affected bacterial adhesion.

The alga Euglena gracilis stimulates Faecalibacterium in the gut and contributes to increased defecation.

The alga Euglena gracilis (E. gracilis) has recently gained attention as a health food, but its effects on human gut microbiota remain unknown. This study aimed to determine the effect of E. gracilis on gut microbiota and defecation due to modulation of microbiota composition in vitro and in vivo. The in vitro model simulating human colonic microbiota revealed that E. gracilis addition stimulated the growth of commensal Faecalibacterium. Further, E. gracilis addition enhanced butyrate production by Faecalibacterium prausnitzii. Paramylon, an insoluble dietary fibre that accumulates in E. gracilis and is the main component of E. gracilis, did not stimulate Faecalibacterium growth in vitro. Daily ingestion of 2 g of E. gracilis for 30 days increased bowel movement frequency as well as stool volume in 28 human participants. Collectively, these findings indicate that E. gracilis components other than paramylon, stimulate the growth of Faecalibacterium to improve digestive health as well as promote defecation by increasing butyrate production.